Scroll-Type Apparatus

ABSTRACT

Scroll-type pumping apparatus comprises a stator ( 104 ) comprising a fixed scroll member ( 106 ) having an end plate with a first spiral wrap ( 118 ) extending therefrom, and an orbital scroll member ( 108 ) having an end plate with a second spiral wrap ( 120 ) extending therefrom to intermesh with the first spiral wrap ( 118 ). A motor drives a drive shaft for generating orbital movement of the orbital scroll member relative to the fixed scroll member ( 106 ). The apparatus comprises a plurality of flexible rods ( 122 ) arranged about the drive shaft and each having one end connected to the orbital scroll member ( 108 ) and another end connected to the stator ( 104 ) to support the orbital scroll member ( 108 ) relative to the stator and to inhibit rotation of the orbital scroll member.

The present invention relates to scroll-type apparatus and, moreparticularly, to scroll-type apparatus for use in vacuum pumps.

Scroll-type apparatus is known for operating compressors or vacuumpumps. In both cases the apparatus comprises two scroll members eachcomprising a flat end plate on which are upstanding strips defining aspiral (or scroll) type structure which interact by placing the scrollmembers together with the respective spiral type structuresinter-engaging and allowing one scroll member to “orbit” relative to theother. In this way it is possible to trap a volume of gas between thescroll members thereby to urge the gas from one end of the respectivespirals to the other. In a vacuum pump in particular the gas enters viaa pump inlet at the periphery of the scroll members and exits via a pumpoutlet at the centre of the scroll members.

FIG. 1 illustrates one known arrangement of such scroll-type apparatusin the form of a vacuum pump 2, which includes a stator 4 comprising afixed scroll member 6. Complimenting the fixed scroll member 6 andintermeshing therewith in a manner known per se is an orbital scrollmember 8. The orbital member 8 is mounted on bearings 10, which aresupported on a crank end 12 of a drive shaft 14 extending from a motor16. Bearings 17 serve to support the drive shaft 14 relative to thehousing 4. Each scroll member 6, 8 includes an end plate to which isattached and from which extends outwardly therefrom a spiral wrap 18,20. The height of each wrap 18, 20 is substantially the same as thedistance between the opposed end plates so that the free edge of eachwrap 18, 20 forms a seal against the face of the complimentary scrollmember end plate. To assist in the sealing process, complaint tip seals(not shown) are commonly provided at the free edge of each wrap 18, 20to take up the axial clearance between the edge of each wrap 18, 20 andthe end plate of the opposing scroll member.

In use, a pumped gas is drawn into the pump 2 from inlet 22 and exitsvia outlet 24 and non-return valve 25. In order to seal the vacuum spacein the housing 4 from ambient atmosphere and the pump drive system, ametal bellows 26 is disposed substantially co-axially with the driveshaft 14. The metal bellows is attached at one end by bolts 28 to theorbital scroll member 8 and at its opposite end to a stationary part 30of the pump by bolts 32. O-rings 29, 31 serve to seal the attachment ofthe metal bellows 26.

By virtue of the torsional stiffness of the metal bellows 26, thebellows 26 also, serves to limit undesirable travel in the circulartranslation of the orbital scroll member 26 and thus maintain thecorrect angular position between the fixed scroll member 6 and theorbital scroll member 8. However, the use of such bellows restricts thedesign of any vacuum pump incorporating such bellows to the dimensionsof adequately sized bellows having the required torsional stiffness andsufficient radial freedom for required crank throw to achieve inpractice an acceptable life.

Furthermore, the use of compliant tip seals to provide axial sealingbetween the scroll members 6, 8 can generate the dust due to erosion oftip seals during use of the pump. Whilst this dust is generally conveyedthrough the outlet 24 together with the exhaust gas, when the pump isswitched off this dust could migrate through the inlet 22 towards theevacuated apparatus, leading to unwanted contamination of the evacuatedapparatus. The tip seals therefore require regular replacement, andtheir use further restricts the design of any vacuum pump incorporatingsuch seals to the dimensions of adequately sized tip seals.

It is an aim of at least the preferred embodiment of the presentinvention to solve these and other problems.

The present invention provides scroll-type pumping apparatus comprisinga stator comprising a fixed scroll member having an end plate with afirst spiral wrap extending therefrom, an orbital scroll member havingan end plate with a second spiral wrap extending therefrom to intermeshwith the first spiral wrap, means for driving the orbital scroll memberto orbit relative to the fixed scroll member, and a plurality offlexible rods each having one end connected to the orbital scroll memberand another end connected to the stator to support the orbital scrollmember relative to the stator.

The use of such rods can provide support of the orbital scroll memberrelative to the stator with a high degree of axial accuracy, thusenabling very close running clearances between the edge of each spiralwrap and the end plate of the opposite scroll member without the needfor tip seals, and so the generation of dust associated with the use oftip seals is avoided.

The rods may also serve to inhibit rotation of the orbital scroll memberrelative to the fixed scroll member, so that there is no requirement fora separate device for inhibiting rotation of the orbital scroll member.Therefore, the present invention also provides use of a plurality ofrods in a scroll-type apparatus having a fixed scroll member and aorbital scroll member, to inhibit rotation of the orbital scroll memberrelative to the fixed scroll member. Whilst a bellows may be provided toseparate a vacuum space from the ambient atmosphere, there is norequirement for the bellows to have a particular torsional stiffness. Asa result, there is a greater freedom of design of a vacuum pumpincorporating the apparatus of the present invention, enabling arelatively small, low cost pump to be provided which has good axialsealing between the scroll members. However, an additional device suchas an Oldham coupling may be provided between the orbital scroll memberand the stator for preventing rotation of the orbital scroll memberrelative to the fixed scroll member.

An abrasive coating may be provided on a surface of at least one of thescroll members. The coating may extend over the surface of the end plateand the spiral wrap of the, or each, scroll member.

The driving means preferably comprises a drive shaft having a crankconnected to the orbital scroll member and positioned such that rotationof the drive shaft about a longitudinal axis thereof causes the orbitalscroll member to orbit about the longitudinal axis. The flexible rodspreferably extend about a longitudinal axis of the drive shaft.

As mentioned above, a flexible member such as a bellows may be providedfor separating a vacuum space in the stator from ambient atmosphere. Theflexible member may be substantially co-axial with, and/or arrangedabout, the flexible rods.

The rods may be formed from a metallic or composite material.

The scroll-type apparatus may be used as either a compressor or as anexpander, and so the present invention further provides scroll-typeapparatus comprising a stator comprising a fixed scroll member having anend plate with a first spiral wrap extending therefrom, an orbitalscroll member having an end plate with a second spiral wrap extendingtherefrom to intermesh with the first spiral wrap, means for driving theorbital scroll member to orbit relative to the fixed scroll member, anda plurality of flexible rods each having one end connected to theorbital scroll member and another end connected to the stator to supportthe orbital scroll member relative to the stator.

Preferred features of the present invention will now be described withreference to the accompanying drawings, in which:

FIG. 1 is a cross-section through a known scroll-type vacuum pump;

FIG. 2 is a simplified cross-section through a first embodiment of ascroll-type vacuum pump;

FIG. 3 is a simplified cross-section through a second embodiment of ascroll-type vacuum pump; and

FIG. 4 is a cross-section through the vacuum pump of FIG. 1 modifiedaccording to the present invention.

With reference to FIG. 2, a first embodiment of a scroll-type apparatusis in the form of a vacuum pump 102, which includes a stator 104comprising a fixed scroll member 106. Complimenting the fixed scrollmember 106 and intermeshing therewith in a manner known per se is anorbital scroll member 108. The orbital member 108 is attached to a crankprovided at one end of the drive shaft 112, which extends from a motor114. Bearings 116 serve to radially support the drive shaft 112 relativeto the stator 104. Each scroll member 106, 108 includes an end plate towhich is attached and from which extends outwardly therefrom a spiralwrap 118, 120. The height of each wrap 118, 120 is substantially thesame as the distance between the opposed end plates so that the freeedge of each wrap 118, 120 forms a seal against the face of thecomplimentary scroll member end plate. An abrasive coating may beprovided on the end plate and wrap of at least one of the scroll members106, 108.

The orbital scroll member 108 is supported axially relative to the fixedscroll member 106 by a plurality of flexible rods 122 provided about thelongitudinal axis of the drive shaft 112. One end of each rod 122 issecured to the stator 104 by any suitable means, for example, adhesiveor bolts, and the other end of each rod is similarly secured to the endplate of the orbital scroll member 108. At least three rods 122 aregenerally required, although any number may be provided. The rods 122may be formed from any suitable material having a stiffness that allowsthe rods 122 to flex to allow the orbital scroll member 108 to orbitabout the longitudinal axis of the drive shaft 112 relative to the fixedscroll member 106. For example, the rods 122 may be formed from metallicmaterial, such as steel, or a composite material, such as an organicmatrix composite material comprising a resin filled with reinforcingparticles and/or fibres. This material is preferably a thermosettingresin, such as epoxy, filled with reinforcing carbon fibres. In thisembodiment, the rods 122 also serve to inhibit rotation of the orbitalscroll member 108 relative to the fixed scroll member 106.Alternatively, an Oldham coupling may be provided between the stator 102and the orbital member 108 to inhibit rotation of the orbital scrollmember 108 relative to the fixed scroll member 106.

In the embodiment shown in FIG. 2, the end plate of the fixed scrollmember 106 is integral with the stator 104. Alternatively, the end plateof the fixed scroll member 106 may be provided in the form of a platemounted on the stator by any convenient method. For example, in thesecond embodiment shown in FIG. 3, the fixed scroll member 106 ismounted on, or integral with, an enclosure 124 for the motor 114, thedrive shaft 112 passing through an aperture provided in the fixed scrollmember 106 and supported therein by bearings 116.

As shown in FIG. 4, the rods 122 may be provided in combination with aflexible member 126 for sealing a vacuum space of the pump from theambient atmosphere, as previously illustrated in FIG. 1, and where likereference numerals indicate the same features as shown in FIG. 1. In theexample shown in FIG. 4, the rods 122 are external to the flexiblemember, preferably provided in the form of a bellows 126, although, asan alternative, the bellows 126 may surround the rods 122. In thisexample, unlike the bellows 26 of the prior art shown in FIG. 1, thebellows 126 are not required to have a torsional stiffness necessary toinhibit rotation of the orbital scroll member 8, as this functionalityis provided by the rods 122, and so the bellows 126 may be formed fromless rigid, and therefore less expensive, material.

In a further refinement of the design, the stiffness of the rods 122 issuch that the natural frequency of the orbital scroll member 8, 108 in atranslational (x or y, or combination of both, i.e. circular) mode ismatched to the operating speed of the pump 2, 102. In this case radialforces on the drive crank are greatly reduced, allowing a smallerbearing to be used. Damping devices may also be used to give a flatterresponse curve and make tuning of the pump more tolerant.

1. Scroll-type pumping apparatus comprising: a stator comprising: afixed scroll member having an end plate with a first spiral wrapextending therefrom, an orbital scroll member having an end plate with asecond spiral wrap extending therefrom to intermesh with the firstspiral wrap, a drive shaft for driving the orbital scroll member toorbit relative to the fixed scroll member, and a plurality of flexiblerods each having one end connected to the orbital scroll member andanother end connected to the stator to support the orbital scroll memberrelative to the stator.
 2. The apparatus according to claim 1 whereinthe drive shaft comprises a crank connected to the orbital scroll memberand positioned such that rotation of the drive shaft about alongitudinal axis thereof causes the orbital scroll member to orbitabout the longitudinal axis.
 3. The apparatus according to claim 2wherein the flexible rods extend about a longitudinal axis of the driveshaft.
 4. The apparatus according to claim 1 comprising a flexiblemember for separating a vacuum space in the stator from ambientatmosphere.
 5. The apparatus according to claim 4 wherein the flexiblemember is substantially co-axial with the flexible rods.
 6. Theapparatus according to claim 4, wherein the flexible member comprises abellows.
 7. The apparatus according to claim 4, wherein the flexiblerods are arranged about the flexible member.
 8. The apparatus accordingto claim 1 wherein the rods are formed from a metallic material.
 9. Theapparatus according to claim 1 wherein the rods are formed from acomposite material.
 10. The apparatus according to claim 1 wherein theplurality of rods inhibit rotation of the orbital scroll member relativeto the fixed scroll member.
 11. (canceled)